Area Forecast Discussion
Issued by NWS Portland, OR

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FXUS66 KPQR 012151
AFDPQR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PORTLAND
250 PM PDT MON JUN  1 2015

.SYNOPSIS...UPPER LEVEL LOW PRESSURE CONTINUES TO DRIFT NORTHWARD
ALONG THE WILLAMETTE VALLEY TODAY...WITH NUMEROUS SHOWERS WRAPPING
AROUND THE SYSTEM. DEEP ONSHORE FLOW IS KEEPING THE REMAINDER OF
SOUTHWEST WASHINGTON AND NORTHWEST OREGON COOL AND CLOUDY...AND
GENERALLY TOO STABLE FOR THUNDERSTORMS. COOL AND SHOWERY WEATHER WILL
CONTINUE INTO TUESDAY...WITH SHOWERS ENDING WEDNESDAY. THEN A STRONG
UPPER LEVEL RIDGE OF HIGH PRESSURE IS EXPECTED TO BUILD OVER THE
PACIFIC NORTHWEST LATER THIS WEEK AND THROUGH THE WEEKEND... POSSIBLY
BRINGING THE WARMEST TEMPERATURES SO FAR THIS YEAR.

&&

.SHORT TERM...TONIGHT THROUGH THURSDAY...SATELLITE LOOP SHOWS A
WELL-DEFINED CIRCULATION OVER MUCH OF SOUTHWEST WASHINGTON AND
NORTHWEST OREGON...PRESENTLY CENTERED A FEW MILES E-SE OF PORTLAND.
BANDS OF SHOWERS ARE WRAPPING AROUND THIS SYSTEM...BRINGING AS MUCH
AS 0.25-0.50 INCH OF RAIN TO AREAS THAT ARE AFFECTED. WHILE THERE IS
SOME CONVECTIVE NATURE TO THESE BANDS...THE TOPS ARE HAVING A TOUGH
TIME GETTING MUCH ABOVE 20 KFT...LIMITING THE LIGHTNING POTENTIAL. IT
IS A DIFFERENT STORY EAST OF THE CASCADES...WHERE MORE SUNBREAKS HAVE
DESTABILIZED THE LOW LEVELS AND ALLOWED FOR SOME SURFACE-BASED
INSTABILITY. HOWEVER FOR AREAS WEST OF THE CASCADES DEEP ONSHORE FLOW
IS LIMITING SURFACE HEATING...WITH ANY CONVECTION ALMOST ENTIRELY
DEPENDENT ON SYNOPTIC LIFT FROM THE LOW PRESSURE SYSTEM. WILL LEAVE A
SLIGHT CHANCE OF THUNDER IN THE CASCADES NORTH OF MOUNT HOOD THROUGH
THIS EVENING...BUT MY GUT FEELING IS THAT THUNDERSTORMS ARE DONE IN
OUR CWA FOR THE TIME BEING.

MEANWHILE LARGE-SCALE ONSHORE PRESSURE GRADIENTS CONTINUE TO RAMP UP.
NORTH BEND TO SPOKANE PRESSURE GRADIENTS ARE UP TO NEAR +9 MB...
WHICH CONTINUES TO USHER A DEEP MARINE INFLUENCE ALL THE WAY UP TO
THE CASCADE CREST. 18Z NAM CONTINUES TO SHOW ONSHORE GRADIENTS
UPWARDS OF +10 MB TUE AFTERNOON...WHICH SHOULD RESULT IN EXTENSIVE
LOW CLOUDINESS TUESDAY AS WELL. THIS SHOULD HOLD TEMPS IN THE LOWER
TO MID 60S EVEN FOR THE INLAND VALLEYS. CONTINUED CYCLONIC FLOW
SHOULD PROMOTE MORE SHOWER ACTIVITY THROUGH TUESDAY...SO KEPT POPS
HIGH AS A RESULT. NAM/GFS CONTINUE TO STRENGTHEN THE CAP ABOVE
600-500 MB...SO IT WILL BE DIFFICULT FOR SHOWERS TO HAVE TOPS MUCH
ABOVE 15 KFT ACROSS OUR DISTRICT TUESDAY. THEREFORE IT APPEARS
THUNDER IS UNLIKELY TUE AFTERNOON ON OUR SIDE OF THE CREST...AS IT
WILL BE A TALL ORDER TO WARM SURFACE PARCELS SUFFICIENTLY TO BREAK
THIS CAP.

WITH LITTLE FORCING IT APPEARS SHOWERS SHOULD BE DIURNALLY DRIVEN FOR
THE MOST PART TUESDAY...AND SHOWERS SHOULD DECREASE AFTER SUNSET.
FLOW REMAINS CYCLONIC AND THERE IS ENOUGH MOISTURE AND LOW-LEVEL
INSTABILITY TO KEEP SOME POPS IN WEDNESDAY...ESPECIALLY IN THE
AFTERNOON AND NORTH OF SALEM. WITH PLENTY OF CLOUDS AND 850 MB TEMPS
REMAINING NEAR +5 DEG C IT APPEARS HIGHS WED WILL ALSO FALL SHORT OF
EARLY JUNE NORMALS. HOWEVER...MODELS ARE SUGGESTING DEVELOPMENTS WILL
BEGIN TO OCCUR WEDNESDAY WHICH WILL START A TRANSITION TOWARD MUCH
WARMER WEATHER LATER IN THE WEEK THROUGH THE WEEKEND.

WHILE THERE REMAINS SOME UNCERTAINTY...MODELS ARE SHOWING IMPRESSIVE
AGREEMENT ON A SIGNIFICANT WARM SPELL DEVELOPING BY THE WEEKEND. THIS
STARTS WITH THE SHEARING OFF OF A SHORTWAVE APPROACHING THE PAC NW
WEDNESDAY...THEN THE FORMATION OF A CUTOFF LOW NEAR CALIFORNIA
THURSDAY. THIS SHOULD TURN THE FLOW MORE NORTHERLY...POSSIBLY
NORTHEASTERLY...CONSIDERABLY DRYING OUT THE BOUNDARY LAYER BY
THURSDAY AFTERNOON. ANY MORNING CLOUDS THURSDAY ARE EXPECTED TO CLEAR
OUT EXCEPT PERHAPS ALONG THE WA COAST. DECIDED TO LEAVE A SLIGHT
CHANCE OF THUNDER IN THE LANE COUNTY CASCADES THU AFTERNOON...TO
MATCH OUR NEIGHBORS JUST IN CASE THE UPPER LOW CUTS OFF A BIT FURTHER
NORTH THAN THE 12Z GFS/ECMWF SUGGEST. HOWEVER THURSDAY SHOULD BE THE
FIRST REAL SUNNY DAY THIS WEEK...AND PROBABLY THE FIRST OF SEVERAL AS
WE HEAD INTO WHAT COULD BE A SIGNIFICANT WARM SPELL.  WEAGLE

.LONG TERM...THURSDAY NIGHT THROUGH MONDAY...12Z GFS AND ECMWF BOTH
SHOW THE DEEP UPPER LEVEL TROUGH GETTING PINCHED OFF AND BECOMING A
CUT-OFF LOW OVER NORTHERN CALIFORNIA LATE THURSDAY. AS THIS CUT-OFF
LOW DIGS FURTHER SOUTH INTO CALIFORNIA...AN UPPER LEVEL RIDGE
DEVELOPS OVER THE EAST PACIFIC...ATTEMPTING TO SET UP A REX BLOCK
OVER WESTERN CONUS FRIDAY AND THROUGH THE WEEKEND. EXPECT GUSTY
NORTHERLY WINDS ALONG THE COAST...PERIODS OF MORNING CLOUDS FOR
COASTAL LOCATIONS AND ALONG THE LOWER COLUMBIA RIVER...AND
TEMPERATURES LIKELY WARMING WELL ABOVE AVERAGE TOWARDS THE WEEKEND.
MODELS ARE SHOWING 850 MB TEMPERATURES HOVERING AT OR JUST ABOVE 20
DEG CELSIUS FOR SATURDAY AND SUNDAY...WHICH WOULD ALLOW SURFACE
TEMPERATURES TO FLIRT AT OR JUST ABOVE 90 DEG FAHRENHEIT. /27

&&

.AVIATION...CONTINUED MIX OF MVFR AND VFR CIGS THIS AFTERNOON AS
LOW PRESSURE TROUGH CONTINUES TO LIFT NORTHWARD THROUGH THE AREA.
ONE EXCEPTION IS THE KONP...WHERE IFR CIGS REMAIN. AS OF 21Z...A
BAND OF HEAVIER SHOWERS IS NEAR THE COLUMBIA RIVER WITH ANOTHER
ALONG A KTMK-KSLE LINE ROTATING NORTHWARD. EXPECT SLIGHT
IMPROVEMENT FOR MOST LOCATIONS FROM S TO N THIS EVENING AS
SHOWERS DECREASE AND CIGS INCREASINGLY IMPROVE TO VFR. ANOTHER
TROUGH OF LOW PRESSURE ENTERS THE REGION OVERNIGHT INTO TOMORROW...SO
EXPECT ANOTHER PUSH OF MARINE STRATUS AFT 05Z TONIGHT ALONG WITH
ANOTHER ROUND OF SHOWERS TO PUSH ONSHORE WITH LOWERING MVFR CIGS
AROUND 1500-2000 FT AND PERHAPS REDUCED VSBYS IN RAIN SHOWERS.
THIS LIKELY REACHES THE WILLAMETTE VALLEY BY 12Z AND CONTINUES
THROUGH TUE AFTERNOON. WITH CONTINUED ONSHORE LOW LEVEL FLOW
ALONG THE CENTRAL COAST...EXPECT IFR TO LOW MVFR CIGS TO CONTINUE
AT KONP.

KPDX AND APPROACHES...CIGS LIKELY REMAIN VFR THIS EVENING WITH
LINGERING SHOWERS THROUGH TONIGHT. SURFACE WINDS E-SE THROUGH
23Z...THEN BECOMING S-SW AS LOW PRESSURE TROUGH PUSHES FURTHER
NORTHWARD. ANOTHER TROUGH MOVES INTO THE REGION OVERNIGHT WITH
LOWERING CIGS TO AROUND 2000 FT AFT 11Z ALONG WITH ANOTHER ROUND
OF SHOWERS. MVFR CIGS LIKELY CONTINUE THROUGH MIDDAY TUE BEFORE
GRADUALLY TRENDING TOWARD LOWER VFR RANGE.


&&

.MARINE...SOUTH WINDS AROUND 15 KT ACROSS THE WATERS THIS MORNING.
WINDS WILL REMAIN 15 KT OR LESS AND GENERALLY SOUTH-SOUTHWEST
THROUGH MIDWEEK. MODELS REMAIN IN GOOD AGREEMENT WITH RESPECT TO
DEVELOPING SMALL CRAFT ADVISORY STRENGTH NORTH WIND OVER THE
WATERS BEGINNING THURSDAY EVENING OR EARLY FRIDAY AND CONTINUING
THROUGH THE WEEKEND. COULD SEE AFTERNOON AND EVENING WIND GUSTS UP
TO 25 TO 30 KT DURING THIS PERIOD...ESPECIALLY OVER THE SOUTHERN
WATERS.

SEAS TO REMAIN 4 FT OR LESS FOR THE NEXT FEW DAYS. MODEL GUIDANCE
SUGGEST MULTIPLE SMALL SWELLS FT SWELL SETS THROUGH MUCH OF THE
WEEK...ONE SOUTHERLY AND ANOTHER WESTERLY. EITHER OF THESE MAY BE
THE DOMINANT SWELL AT TIMES. EXPECT INCREASING FRESH SWELL COMPONENT
DEVELOPING BY FRIDAY WITH STRONGER NORTH WINDS...BUILDING OVERALL
WAVE HEIGHTS TO AROUND 7 FEET.

&&

.PQR WATCHES/WARNINGS/ADVISORIES...
OR...NONE.
WA...NONE.
PZ...NONE.

&&

$$

INTERACT WITH US VIA SOCIAL MEDIA
WWW.FACEBOOK.COM/NWSPORTLAND
WWW.TWITTER.COM/NWSPORTLAND

THIS DISCUSSION IS FOR NORTHWEST OREGON AND SOUTHWEST WASHINGTON
FROM THE CASCADE CREST TO 60 NAUTICAL MILES OFFSHORE. THE AREA IS
COMMONLY REFERRED TO AS THE FORECAST AREA.


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